USGS Professional Pages
Although my specialty is in surface water/groundwater exchange processes, here at the Branch of Geophysics we work on a wide range of pressing hydrological issues around the world. The Branch of Geophysics supports state water science centers when hydro-geophysical tools and training are required, and we collaborate with academic institutions on pioneering water research. One of our central missions at the Branch is training and method development, so we travel around the country giving workshops and field testing new methods. So far I have primarily been involved with:
· 2012, 2014 expeditions to the Yukon Flats, Alaska as field team leader to characterize permafrost extent and lake budgets using seismic, electrical, radar, thermal and mechanical methods, and subsequent modeling of unsaturated permafrost dynamics.
· Innovative characterization of endangered shellfish habitat in the Delaware River using electrical and thermal methods including modified fiber-optic Distributed Temperature Sensing (FO-DTS) and infrared technology.
· Modeling dual-domain mass transfer of uranium contaminated groundwater in Colorado involving the novel use of combined electrical and chemical methods to inform parameter estimation; investigation of uranium contaminated groundwater discharge points in Wyoming
· Installation of sea water intrusion monitoring network on a remote Pacific atoll to monitor the effects of climate change and sea level rise on atoll fresh water resources
· Refining and applying various infrared, fiber-optic, and discrete-sensor heat tracing field methods and modeling approaches for the study of preferential fish habitat in PA, MA, and VA
· Study of exchange with less-mobile porosity in streambed materials and the subsequent effects on N cycling
· Planning and creating teaching materials for USGS training workshops (n=5) on the topics of hydrogeopohysics and surface water/groundwater exchange
My Science Topics
Surface water/groundwater exchange processes
Fundamentally, streams represent physical conduits of water across gradients, yet a more holistic definition reveals steam corridors support a mosaic of living communities in a blend of surface and ground waters. The physical and biogeochemical patterns these dynamic systems support affect habitat and water quality, which directly impacts the human experience. Our understanding of stream and groundwater interactions is at a time of rapid expansion due to an increase in environmental awareness, accountability, and emerging techniques which can be used to decipher underlying controls and develop predictive relationships. Water temperature has been used as a qualitative environmental tracer during the forging of this country from Lewis and Clarks pioneering spatial explorations to Thoreau’s revolutionary scientific investigations; yet only very recent modeling and technological advancements have allowed us to apply these principles in a more distributed quantitative fashion. The resulting description of physical flow dynamics can be combined with innovative biogeochemical assessments to determine the fundamental linkages between inert and living processes along the stream corridor.
The magnitude and spatial distribution of groundwater inflows to streams is a known control on stream water quality. These inflows can be recognized and evaluated through a variety of methods, each with it’s own sensitivity and basic requirements. One such method is using the temperature differential between surface and groundwaters to both locate and quantify groundwater inputs. The emerging method of fiber-optic distributed temperature sensing (FO-DTS) uses the temperature dependent backscatter of light along fiber optic cables to determine temperature at high spatial and temporal resolution, essential creating continuous thermometers that may be applied to aquatic systems over a broad range of spatial scales. We have modified this technology to create high spatial resolution (0.008-0.014 m) sensors that can be deployed in the water column to monitor thermal refugia, and the subsurface to track water flux. We have developed software techniques to model subsurface temperature data to quantify vertical fluid flux (e.g. VFLUX and 1DTempPro). Surface FO-DTS deployments can be augmented or at times replaced with infrared remote sensing which we perform with several hand held units.
The “hyporheic zone” describes where stream water temporarily enters the sub-surface, which is known to be biogeochemically reactive, before potentially mixing with shallow groundwaters and returning to the stream. This flux across the streambed interface has driven much recent research, but the intrinsic spatial and temporal variability have proven a challenge to define. As mentioned above, custom high spatial resolution FO-DTS can be installed in the streambed to monitor the propagation of diurnal temperature signals and which are analyzed with one-dimensional conduction-advection-dispersion models to determine the vertical component of hyporheic flux. Often the real power of such refined descriptions of the physical hyporheic system is that they can be directly compared to ambient biogeochemical data collected in coincident vertical profiles to evaluate the physical controls on streambed chemistry and nutrient cycling.
I hope this knowledge will serve to improve the management of, and appreciation for, the veins of our shared landscape.
11 Sherman Place
Storrs, CT 06279
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